My friend did the FN rush last Sunday. we got there around 11:30-ish for the 12 pm BO opening, and while there were plenty of people in line already they still got very good seats, even though it was the Holidays. It was a 2-show day though (they added an evening performance & she got tickets for that), a matinee might be a little harder considering it's become such a family. Maybe try for 11 instead. It'll probably depend on how cold it is, too. I image families might not do the rush if it's freezing out.
Keep it mind it's only ONE ticket per ID, not 2 like most other rushes.